Remove obsolete/harmful overriding of documentation CSS
I haven't noticed any effect of the `.page-tools` part of the CSS code. 927406cc introduced this code in 2014 - it must have become obsolete at some point after that. Forcing white body background affects the navigation menu at the bottom of most documentation pages. I find light-gray text on white background significantly less readable than the default light-gray on black. Perhaps the situation was different in 2016 when ec8ca05f forced the white background. This overriding of CSS has not been working for 5 years since 08383711, so I don't think anyone would miss it.